The present invention relates to a multilayer tube which can in particular be advantageously used in medical applications whose requirements are very demanding.
Several specific polymers have already been proposed in order to satisfy these requirements. Thus, for example, it has already been proposed to use copolyesterethers manufactured from poly(tetramethylene oxide) glycol, 1,4-cyclohexanedicarboxylic acid and 1,4-cyclohexanedimethanol. The manufacture of such copolymers (called hereinafter "PCCE") is, for example, described in U.S. Pat. No. 4,349,469.
The requirements imposed on tubes for medical use are, in particular, flexibility, (medical-grade) nontoxicity, transparency and high-frequency (HF) weldability requirements. The manufacture of such tubes consequently poses very specific problems, which means that polymers suitable for manufacturing films, for example, are not necessarily suitable for manufacturing tubes.
Thus, PCCEs which are suitable for manufacturing films are ill-suited for manufacturing tubes because of their rapid crystallization, which has a negative effect on the transparency and on the flexibility. Certainly, rapid (quench) cooling may help to alleviate these problems, but this solution is effective only for extremely small thicknesses, for example, thicknesses of less than 200 .mu.m. A quench would thus constitute a satisfactory solution only in the manufacture of extremely thin tubes, but is not by itself sufficient when the manufacture of tubes for medical use is envisaged, which generally have a thickness of 500 .mu.m. Furthermore, PCCEs are relatively not very polar and therefore ill-suited to HF welding.